A West Australian drilling consultant who is helping in the extraordinary mine rescue in northern Chile says finding the 33 men alive was a complete surprise.

Kelvin Brown flew from Perth to join the international rescue effort to find the miners, who are trapped in a shaft 700 metres below the surface.

The miners are trapped seven kilometres inside the winding mine and rescuers say it may take months to get them out.

Mr Brown says he did not expect to find the men still alive after being stuck underground for more than two weeks.

And he said rescuers were shocked when they pulled a drill bit out of a hole drilled into a refuge chamber only to find notes stuck on the end of it with insulation tape.

"The guys underground quickly got pen and paper and hurriedly wrote several notes, and they used insulation tape and they taped it onto.... a hammer that was raised to the surface. That was very ecstatic and no-one was expecting that," he said.

Mr Brown says the hardness of the local rock means it will take months to drill a hole big enough to rescue the trapped men.

"What has to happen now is a very large diameter hole has to be drilled from the surface some 688 metres to where the rescue chamber is, and this could take several months," he said.

He says a narrow tube is being used to pass the men medical supplies, food and water, and the worst problem they will face in the meantime is boredom.

Andre Sougarret, who is heading up the drilling effort, said engineers would drill two shafts; one to ensure ventilation and communication in the coming months, and another wider one to extract the miners via pulley.

Engineers are transporting a more powerful drill from another mine and must decide where to bore the larger hole without risking further cave-ins.

The miners have not been told how long it will take, and could potentially be stuck until Christmas.

Officials made radio contact with the miners on Monday and found they were in remarkably good condition and spirits despite the ordeal.

Tanks of water and ventilation have helped them to survive but they have had very limited food supplies and health officials estimate they may have lost about eight kilograms each.

Relatives have written letters to send down the shaft to the miners to help boost morale during the long wait ahead.

The accident in the small gold and copper mine has turned a spotlight on mine safety in Chile, the world's top copper producer, although accidents are rare at major mines.

The government says the San Jose mine, owned by local private company Compania Minera San Esteban Primera, has suffered a series of mishaps. Sixteen workers have been killed in recent years.